Methods and systems for CSI-RS port selection for CSI-reporting

ABSTRACT

According to certain embodiments, a method in a network node, is disclosed. The method comprises selecting a sub set from a predetermined set of P CSI-RS ports for receiving channel information. The network node comprises an antenna array with controllable polarization. Each CSI-RS port corresponds to a combination of a set of resource elements and an antenna port of said antenna array. The predetermined set comprises a first number P1 of CSI-RS ports with a first polarization state and a second number P2 of CSI-RS ports with a second polarization state. The first and second polarization states are distinct. The method further comprises populating the subset with Q CSI-RS pons in such mariner that the ratio of CSI-RS pons respectively having the first and second polarization states is equal to the ratio of the first and second numbers.

PRIORITY

This application is a continuation, under 35 U.S.C. § 120 of Ser. No.15/032,60 which is U.S. National Stage Filing under 35 U.S.C. § 371 ofInternational Patent Application Serial No. PCT/SE2016/050241 filed Mar.23, 2016, and entitled ‘Methods And Systems For CSI-RS Port SelectionFor CSI-Reporting” which claims priority to U.S. Provisional PatentApplication No. 62/251,574 filed Nov. 5, 2015, of which are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates, in general, to wireless communicationsand, more particularly, to CSI-RS port to resource mapping and selectionof a subset of CSI-RS ports for CSI reporting.

BACKGROUND

FIG. 1 illustrates the basic Long Term Evolution (LTE) downlink physicalresource. LTE uses Orthogonal Frequency Division Multiplexing (OFDM) inthe downlink and Discrete Fourier Transform (DFT)-spread OFDM in theuplink. The basic LTE downlink physical resource can thus be seen as atime-frequency grid, where each resource element (or time/frequencyresource element, TFRE) corresponds to one OFDM subcarrier during oneOFDM symbol interval.

FIG. 2 illustrates the LTE time-domain structure. In the time domain,LTE downlink transmissions are organized into radio frames of 10 ms.Each radio frame consists often, equally-sized sub frames of lengthT_(subframe)=1 ms.

Furthermore, the resource allocation in LTE is typically described interms of resource blocks (RBs), where a resource block corresponds toone slot (0.5 ms) in the time domain and 12 contiguous subcarriers inthe frequency domain. Resource blocks are numbered in the frequencydomain, starting with 0 from one end of the system bandwidth.

FIG. 3 illustrates an example downlink subframe. Downlink transmissionsare dynamically scheduled. In other words, in each subframe the basestation transmits control information about to which terminals data istransmitted and upon which resource blocks the date is transmitted inthe current, downlink subframe. This control signaling is typicallytransmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe. Forexample, FIG. 3 illustrates a downlink system with 3 OFDM symbols ascontrol.

LTE uses hybrid-ARQ, where, after receiving downlink data in a subframe,the terminal attempts to decode it and reports to the base stationwhether the decoding was successful. If the decoding is successful, theterminal reports an acknowledgement (ACK) to the base station.Conversely, if the decoding is not successful, the terminal reports annegative acknowledgement (NAK) to the base station. In case of anunsuccessful decoding attempt, the base station can retransmit theerroneous data.

Uplink control signaling from the terminal to the base station includeshybrid-ARQ acknowledgements for received downlink data. Uplink controlsignaling may also include terminal reports related to the downlinkchannel conditions, used as assistance for the downlink scheduling.Additionally, uplink control signaling may include scheduling requests,indicating that a mobile terminal needs uplink resources for uplink datatransmissions. If the mobile terminal has not been. assigned an uplinkresource tor data transmission, the L1/L2 control information(Layer-1/Layer-2control information, e.g., channel state information(CSI) reports, hybrid-ARQ acknowledgments, and scheduling requests) istransmitted in uplink resources (resource blocks) specifically assignedfor uplink L1/L2 control on the Physical Uplink Control Channel (PUCCH)

FIG. 4 illustrates uplink L1/L2 control signaling transmission on PUCCH.The uplink resources assigned for uplink L1/L2 control on the PUCCH arelocated at the edges of the total available ceil bandwidth. Each suchresource consists of twelve subcarriers (one resource block) within eachof the two slots of an uplink subframe. In order to provide frequencydiversity, these frequency resources are frequency hopping on the slotboundary (i.e., one “resource” consists of 12 subcarriers at the upperpart of the spectrum within the first slot of a subframe and an equallysized resource at the lower part of the spectrum during the second slotof the subframe or vice versa). If more resources are needed for theuplink L1/L2 control signaling, for example in the case of very largeoverall transmission bandwidth supporting a large number of users,additional resource blocks can be assigned next to the previouslyassigned resource blocks.

As described above, uplink L1/L2 control signaling includes hybrid-ARQacknowledgements. channel state information reports and schedulingrequests. Different combinations of these types of messages are possibleas described below, but to explain the structure for these cases it isbeneficial to discuss separate transmission, of each of the types first,starting with the hybrid-ARQ and the scheduling request. There are threeformats defined for PUCCH, each capable of carrying a different numberof bits. A brief description of PUCCH format 2 is provided below.

In PUCCH format 2, channel state information reports are used to providethe eNodeB with an estimate of the channel properties at the terminal inorder to aid channel-dependent scheduling. A channel state informationreport consists of multiple bits per subframe. PUCCH format 1, which iscapable of at most two bits of information per subframe may not besuitable for this purpose. Transmission of channel state informationreports on the PUCCH is instead handled by PUCCH format 2, which iscapable of multiple information bits per subframe. There are threevariants in the LIE specifications: formats 2; 2a; and 2b. Formats 2aand 2b are used for simultaneous transmission of hybrid-ARQacknowledgements (described in more detail below). For simplicity, theymay all referred to as format 2 herein. The PUCCH format 2 resources aresemi-statically configured.

Multi-antenna techniques can significantly increase the data rates andreliability of a wireless communication system. The performance is inparticular improved if both the transmitter and the receiver areequipped with multiple antennas, which results in a multiple-inputmultiple-output (MIMO) communication channel. Such systems and/orrelated techniques are commonly referred to as MIMO.

The LTE standard is currently evolving with enhanced MIMO support. Acore component in LTE is the support of MIMO antenna deployments andMIMO related techniques. LTE-Advanced supports an x-layer spatialmultiplexing mode for 8 transmit (Tx) antennas with channel dependentprecoding. The spatial multiplexing mode is aimed for high data rates infavorable channel conditions.

FIG. 5 illustrates an example of spatial multiplexing operation. Moreparticularly, FIG. 5 illustrates an example transmission structure ofpreceded spatial multiplexing mode in LTE. As depicted, the informationcarrying symbol vector s is multiplied by an N_(T)×r precoder matrix W,which serves to distribute the transmit energy in a subspace of theN_(T) (corresponding to N_(T) antenna ports) dimensional vector space.The precoder matrix is typically selected from a codebook of possibleprecoder matrices, and typically indicated by means of a precoder matrixindicator (PMI), which specifics a unique precoder matrix in thecodebook for a given number of symbol streams. The r symbols in s eachcorrespond to a layer and r is referred to as the transmission rank. Inthis way, spatial multiplexing is achieved since multiple symbols can betransmitted simultaneously over the same time/frequency resource element(TFRE) The number of symbols r is typically adapted to suit the currentchannel properties.

LTE uses OFDM in the downlink (and DFT precoded OFDM in the uplink) andhence the received N_(R)×1 vector y_(n) over N_(R) receiving antennaports for a certain TFRE on subcarrier n (or alternatively data TFREnumber n) is thus modeled by:y _(n) =H _(n) Ws _(n) +e _(n)where H_(n) is the channel matrix between eNodeB and a UE, W is theprecoding matrix, s_(n) is the transmitted symbol vector, and e_(n) is anoise/interference vector obtained as realizations of a random process.The precoder, W, can be a wideband precoder, which is constant overfrequency, or frequency selective (i.e., different precoders ondifferent subbands).

The precoder matrix is often chosen to match the characteristics of theN_(R)×N_(T) MIMO channel matrix H_(n), resulting in so-called channeldependent precoding. This is also commonly referred to as closed-loopprecoding, and essentially strives for focusing the transmit energy intoa subspace which is strong in the sense of conveying much of thetransmitted energy to the UE. In addition, the precoder matrix may alsobe selected to strive for orthogonalizing the channel, meaning thatafter proper linear equalization at the UE, the inter-layer interferenceis reduced.

The transmission rank, and thus the number of spatially multiplexedlayers, is reflected in the number of columns of the precoder. Forefficient performance, it is important that a transmission rank thatmatches the channel properties is selected.

In LTE Release 10, a new reference symbol sequence was introduced forestimating channel state information, the Channel State InformationReference Signal (CSI-RS). The CSI-RS provides several advantages overbasing the CSI feedback on the cell specific reference signals (CRS),which were used for that purpose in previous releases. First, the CSI-RSis not used for demodulation of the data signal, and thus does notrequire the same density (i.e., the overhead of the CSI-RS issubstantially less). Second, CSI-RS provides a much more flexible meansto configure CSI feedback measurements (e.g., which CSI-RS resource tomeasure on can be configured in a UE specific manner).

By measuring on a CSI-RS, a UE can estimate the effective channel theCSI-RS is traversing (including the radio propagation channel andantenna gains). This implies that if a known CSI-RS signal x istransmitted, a UE can estimate the coupling between the transmittedsignal and the received signal (i.e., the effective channel). Hence ifno visualization is performed in lire transmission, the received signaly can be expressed as:y=Hx+eand the UE can estimate the effective channel H.

Up to eight CSI-RS ports can be configured for a Release 11 UE. That is,the UE can thus estimate the channel from up to eight transmit antennas.

FIGS. 6A-6C illustrate resource element grids. More particularly, FIGS.6A-6C illustrate resource element grids over an RB pair showingpotential positions for Release 9/10 UE specific RS, CSI-RS (marked witha number corresponding to the CSI-RS antenna port), and CRS. The CSI-RSutilizes an orthogonal cover code (OCC) of length two to overlay twoantenna ports on two consecutive REs. As shown in FIGS. 6A-6C, manydifferent CSI-RS patterns are available. For the case of 2 CSI-RSantenna ports, we see that there are 20 different patterns within asubframe. The corresponding number of patterns is 10 and 5 for 4 and 8CSI-RS antenna ports, respectively. For TDD, some additional CSI-RSpatterns are available.

The CSI reference signal configurations are shown in TABLE 6.10.5.2-1below, taken from TS 36.211 v. 12.5.0. For example, the CSI RSconfiguration 5 for 4 antennas ports use (k′, l′)-(9,5) in slot 1 (thesecond slot of the subframe). Using the formulas below, it can bedetermined that port 15,16, use OCC over the resource elements(k,l)=(9,5), (9,6) and ports 17,18 use OCC over resource elements (3,5),(3,6), respectively (assuming PRB index m=0), where k is the subcarrierindex and l is the OFDM symbol index within each slot.

Thee orthogonal cover code (OCC) is introduced below by the factorw_(i)′.

TABLE 6.10.5.2-1 Mapping from CSI reference signal configuration to (k′,l′) for normal cyclic prefix CSI reference Number of CSI referencesignals configured signal 1 or 2 4 8 configuration (k′, l′) n_(s) mod 2(k′, l′) n_(s) mod 2 (k′, l′) n_(s) mod 2 Frame structure type 1 and 2 0 (9, 5) 0 (9, 5) 0 (9, 5) 0  1 (11, 2) 1 (11, 2) 1 (11, 2) 1  2 (9, 2)1 (9, 2) 1 (9, 2) 1  3 (7, 2) 1 (7, 2) 1 (7, 2) 1  4 (9, 5) 1 (9, 5) 1(9, 5) 1  5 (8, 5) 0 (8, 5) 0  6 (10, 2) 1 (10, 2) 1  7 (8, 2) 1 (8, 2)1  8 (6, 2) 1 (6, 2) 1  9 (8, 5) 1 (8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12(5, 2) 1 13 (4, 2) 1 14 (3, 2) 1 15 (2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18(3, 5) 1 19 (2, 5) 1 Frame structure type 2 only 20 (11, 1) 1 (11, 1) 1(11, 1) 1 21 (9, 1) 1 (9, 1) 1 (9, 1) 1 22 (7, 1) 1 (7, 1) 1 (7, 1) 1 23(10, 1) 1 (10, 1) 1 24 (8, 1) 1 (8, 1) 1 25 (6, 1) 1 (6, 1) 1 26 (5, 1)1 27 (4, 1) 1 28 (3, 1) 1 29 (2, 1) 1 30 (1, 1) 1 31 (0, 1) 1$k = {k^{\prime} + {12m} + \left\{ \begin{matrix}{- 0} & {{{{for}\mspace{14mu} p} \in \left\{ {15,16} \right\}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \left\{ {17,18} \right\}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 1} & {{{{for}\mspace{14mu} p} \in \left\{ {19,20} \right\}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 7} & {{{{for}\mspace{14mu} p} \in \left\{ {21,22} \right\}},{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 0} & {{{{for}\mspace{14mu} p} \in \left\{ {15,16} \right\}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 3} & {{{{for}\mspace{14mu} p} \in \left\{ {17,18} \right\}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 6} & {{{{for}\mspace{14mu} p} \in \left\{ {19,20} \right\}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}} \\{- 9} & {{{{for}\mspace{14mu} p} \in \left\{ {21,22} \right\}},{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}}\end{matrix} \right.}$ $l = {l^{\prime} + \left\{ \begin{matrix}l^{''} & \begin{matrix}{{{CSI}\mspace{14mu}{reference}\mspace{14mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 0\text{-}19},} \\{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix} \\{2l^{''}} & \begin{matrix}{{{CSI}\mspace{14mu}{reference}\mspace{14mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 20\text{-}31},} \\{{normal}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix} \\l^{''} & \begin{matrix}{{{CSI}\mspace{14mu}{reference}\mspace{14mu}{signal}\mspace{14mu}{configurations}\mspace{14mu} 0\text{-}27},} \\{{extended}\mspace{14mu}{cyclic}\mspace{14mu}{prefix}}\end{matrix}\end{matrix} \right.}$ $\quad\begin{matrix}{w_{l^{''}} = \left\{ \begin{matrix}1 & {p \in \left\{ {15,17,19,21} \right\}} \\\left( {- 1} \right)^{l^{''}} & {p \in \left\{ {16,18,20,22} \right\}}\end{matrix} \right.} \\{{l^{''} = 0},1} \\{{m = 0},1,\ldots\mspace{14mu},{N_{RB}^{DL} - 1}} \\{m^{\prime} = {m + \left\lfloor \frac{N_{RB}^{\max,{DL}} - N_{RB}^{DL}}{2} \right\rfloor}}\end{matrix}$

For CSI feedback, LTE has adopted an implicit CSI mechanism where a UEdoes not explicitly report, for example, the complex valued elements ofa measured effective channel, but rather the UE recommends atransmission configuration for the measured effective channel. Thus, therecommended transmission configuration implicitly gives informationabout the underlying channel state.

In LTE, the CSI feedback is given in terms of a transmission rankindicator (RI), a precoder matrix indicator (PMI), and one or twochannel quality indicators (CQIs). The CQI/RI/PMI report can be widebandor frequency selective depending on which reporting mode is configured.The RI corresponds to a recommended number of streams that are to bespatially multiplexed and thus transmitted in parallel over theeffective channel. The PMI identifies a recommended precoder (in acodebook which contains precoders with the same number of rows as thenumber of CSI-RS ports) for the transmission, which relates to thespatial characteristics of the effective channel. The CQI represents arecommended transport block size (i.e., code rate) and LTE supports oneor two simultaneous (on different layers) transmissions of transportblocks (i.e., separately encoded blocks of information) to a UE in asubframe. There is thus a relation between a CQI and all SINR of thespatial stream(s) over which the transport block or blocks aretransmitted.

In LTE Release 10, CSI feedback can correspond to multiple downlinkcarriers, in which case CSI feedback such as CQI/PMI/RI can be providedfor each serving cell corresponding to each of the downlink carriers. Inthis context, P antenna ports of an antenna configuration of a networknode are present on the same serving cell, and a CQI/PMI/RI report for Pantenna ports for the cell corresponds to the P antenna ports present onthe serving cell.

In LTE Release 11, CSI processes arc defined such that each CSI processis associated with a CSI-RS resource and a CSI interference measurement(CSI-IM) resource. A UE in transmission mode 10 can be configured withone or more (up to four) CSI processes per serving cell by higherlayers, and each CSI reported by the UE corresponds to a CSI process. AUE may be configured with a RI-reference CSI process for any CSIprocess, such that the reported RI for the CSI process is the same asfor the RI-reference CSI process. This configuration may be used toforce a UE to report the same RI for several different interferencehypotheses, even though another RI would be the best choice for somehypothesis. Furthermore, a UE is restricted to report PMI and RI withina precoder codebook subset configured for each CSI process by higherlayer signaling. This configuration may also be used to force a UE toreport a specific rank for a certain CSI process.

Both aperiodic (i.e., triggered by eNB) and periodic CSI reports aresupported (known as PA-CSI and P-CSI, respectively). CSI reports arealso referred to as CSI feedback, and these terms may be usedinterchangeably herein. In the CSI process, a set of CSI-RS ports areconfigured for which the UE performs measurements. These CSI-RS portsare configured to be periodically transmitted with, for example, 5 ms,10 ms, 20 ms, or any other suitable periodicity. The periodic CSI reportuses PUCCH format 2 (or its variants 2a, 2b), has a configuredperiodicity as well (e.g., 20 ms), and is a narrow bit pipe containingat most 11 bits.

Recent development in 3GPP has led to the discussion of two-dimensionalantenna arrays. where each antenna element has an independent phase andamplitude control, thereby enabling beamforming both in the vertical andthe horizontal dimensions. Such antenna arrays may be at least partiallydescribed by the number of antenna columns corresponding to thehorizontal dimension N_(h), the number of antenna rows corresponding tothe vertical dimension N_(v), and the number of dimensions correspondingto different polarizations N_(p). Thus, the total number of antennas isN=N_(h)N_(v)N_(p).

FIG. 7 illustrates an example of a two-dimensional antenna array ofcross-polarized antenna elements. More particularly, FIG. 7 illustratesan example of an antenna with N_(h)=4 horizontal antenna elements andN_(v)=8 vertical antenna elements. It furthermore consists ofcross-polarized antenna elements, meaning that the number ofpolarization states N_(p)=2. Such an antenna can be denoted as an 8×4antenna array with cross-polarized antenna elements. The right hand sideillustrates an example port layout, with 2 vertical ports and 4horizontal ports, which could for instance be obtained by virtualizingeach port by 4 vertical antenna elements. Hence, assumingcross-polarized ports are present, the UE will measure 16 antenna portsin this example.

From a wireless device perspective, however, the actual number ofantenna array elements is not visible to the wireless device, but ratherthe antenna ports, where each port corresponds to a CSI referencesignal. The wireless device can thus measure the channel from each, ofthese ports. Therefore, we introduce a 2D port layout described by thenumber of antenna, ports corresponding to the horizontal dimensionM_(h), the number of antenna rows corresponding to the verticaldimension M_(v)and the number of dimensions corresponding to differentpolarizations M_(p). The total number of antenna ports is thusM=M_(h)M_(v)M_(p). The mapping of these ports onto the N antennaelements is an eNB implementation issue, and thus not visible by thewireless device. The wireless device does not even know the value of N;it only knows the value of the number of ports M.

Precoding may be interpreted as multiplying the signal with differentbeamforming weights for each antenna port prior to transmission. Atypical, approach is to tailor the precoder to the antenna form factor(i.e., taking into account M_(h), M_(v) and M_(p) when designing theprecoder codebook.

A common approach when designing precoder code-books tailored for 2Dantenna arrays is to combine precoders tailored for a horizontal arrayand a vertical array of antenna ports, respectively, by means of aKronecker product. This means that (at least part of) the precoder canbe described as a function of:W _(H) ⊗W _(V)where W_(H) is a horizontal precoder taken from a (sub)-codebook X_(H)containing N_(H) codewords. Similarly, W_(V) is a vertical precodertaken from a (sub)-codebook X_(V) containing N_(V) codewords. The jointcodebook, denoted by H_(H)⊗X_(V), thus contains N_(H)·N_(V) codewords.The codewords of X_(H) are indexed with k=0, . . . , N_(H)−1, thecodewords of X_(V) are indexed with l=0, . . . , N_(V)−1, and thecodewords of the joint codebook X_(H)⊗X_(V) are indexed with m=N_(V)·k+l(meaning that m=0, . . . , N_(H)·N_(V)−1).

For Release 12 wireless devices and earlier, only a codebook feedbackfor a ID port layout, is supported, with 2, 4 or 8 antenna ports. Hence,the codebook is designed assuming these pons are arranged on a straightline.

A method has been proposed to use measurements on fewer CSI-RS ports forperiodic CSI reports than measurements for the aperiodic CSI reports. Inone scenario, the periodic CSI report framework is identical to thelegacy terminal periodic CSI report framework. Hence, periodic CSIreports with 2, 4 or 8 CSI-RS ports are used for the P-CSI reporting,and additional ports are used for the A-CSI reporting. From the UE andeNB perspective, the operations related to periodic CSI reporting isidentical to legacy operation. The lull, large 2D port layout CSImeasurements of up to 64 ports or even more is only present in theaperiodic reports. Since A-CSI is carried over PUSCH the pay load can bemuch larger than the small 11-bit limit of the P-CSI using PUCCH format2.

It has been agreed that for 12 or 16 ports, CSI-RS resources for class A(or non-precoded CSI-RS) CSI reporting is composed as an aggregation ofK CSI-RS configurations each with N ports. In case of CDM-2, the KCSI-RS resource configurations indicate CSI-RS RE locations according tolegacy resource configurations in TS 36.211. For 16 ports: (N,K)=(8,2)or (2,8). For 12 ports: (N,K)=(4,3), (2,6). The ports of the aggregatedresource are as follows:

The aggregated port numbers are 15, 16, . . . 30 (for 16 CSI-RS ports)

The aggregated port numbers arc 15, 16, . . . 26 (for 12 CSI-RS ports).

For a given P antenna ports, the Release 10 and 12 precoding codebooksare designed so that the P/2 first antenna ports (e.g., 15-22 for P=16)should map to a set of co-polarized antennas and the P/2 last antennaports (e.g., 23-30 for P-16) are mapped to another set of co-polarizedantennas, with an orthogonal polarization to the first set. For example,the first subset is associated with a first length-P/2vector of alength-P precoding vector in a codebook. The second subset is associatedwith a second length-P/2 vector of the length-P precoding vector,wherein the second length-P/2 is obtained by scaling the firstlength-P/2 vector by a complex number. This is thus targetingcross-polarized antenna arrays, or more generally, antenna arrays withat last two distinct polarization states,

FIG. 8 illustrates the port numbering for P=8 antenna ports. Thecodebook principles for the rank 1 case are that a DFT “beam” vector ischose n for each set of P/2 ports and a phase shift with QPSK alphabetis used to co-phase the two sets of antenna ports. A rank 1 codebook isthus constructed as:

$\begin{pmatrix}a \\{ae}^{i\;\omega}\end{pmatrix}\quad$where a is a length P/2 vector that forms a beam for the first andsecond polarizations, respectively, and ω is a co-phasing scalar thatco-phases the two orthogonal polarizations.

SUMMARY

According to certain embodiments, a method in a network node isdisclosed. The method comprises selecting a subset from a predeterminedset of P CSI-RS ports for receiving channel information. The networknode comprises an antenna array with controllable polarization. EachCSI-RS port correspond to a combination of a set of resource elementsand an antenna port of said antenna array. The predetermined setcomprises a first number P₁ of CSI-RS ports with a first polarizationstate and a second number P₂ of CSI-RS ports with a second polarizationstate. The first and second polarization states are distinct. The methodfarther comprises populating the subset with Q CSI-RS ports in suchmanner that the ratio of CSI-RS ports respectively having the first andsecond polarization states is equal to the ratio of the first and secondnumbers.

According to certain embodiments, a method in a wireless device servedby a network node of a wireless communication network is provided. Thenetwork node is equipped with P=8 or P>8 antenna ports for transmittingsignals to the wireless device. The method includes receiving, from thenetwork node, a CSI-RS setup that includes K CSI-RS configurations eachwith N CSI_RS ports and an antenna configuration of the network nodewith P antenna ports. A subset of Q antenna ports is determined from theP antenna ports. Channel information is measured based on the referencesignals associated with the subset of antenna ports. The measure channelinformation is reported to the network node.

According to certain embodiments, a method, in a wireless device of awireless communication network is provided. The wireless device isserved by a plurality of network nodes, and each network node includesan antenna array. The method includes receiving a reference signal in aspecific set of resource elements from a first network node while beingserved by the first network node. Feedback information is transmitted tothe first network, node. The reference signal or the combination of thereference signal and the set of resource elements is indicative of anidentifier. While being served by a second network node distinct, fromthe first, network node, a reference signal in said set of specificresource elements is received from the second network node. Feedbackinformation is transmitted to the second network node, and the referencesignal or the combination of the reference signal and the set ofresource elements is indicative of an identifier. The reference signalis received with different beamforming from the first and second networknodes in spite of the equality of the identifiers.

According to certain embodiments, a network node is provided. Thenetwork node includes an antenna array with controllable polarization,and one or more processors. The one or more processors are configured toselect a subset from a predetermined set of P CSI-RS ports for receivingchannel information, wherein each CSI-RS port corresponds to acombination of a set of resource elements and an antenna port of saidantenna array. The predetermined set comprises a first number P₁ ofCSI-RS ports with a first polarization state and a second number P₂ ofCSI-RS ports with a second polarization state, the first and secondpolarization states being distinct. The one or more processors arefurther configured to populate the subset with Q CSI-RS ports in suchmanner that the ratio of CSI-RS ports respectively having the first andsecond polarization states is equal to the ratio of the first and secondnumbers

According to certain embodiments, a wireless device configured to beserved by a network node in a wireless communication network isprovided. The network node is equipped with P=8 or P>8 antenna ports fortransmitting signals to the wireless device. The wireless deviceincludes one or more processors. The one or more processors areconfigured to receive, from the network node, a CSI-RS set up comprisingK CSI reference signal configurations each with N CSI-RS ports and anantenna configuration of the network nods with P antenna ports. The oneor more processors are further configured to determine a subset of Qantenna ports from the P antenna ports and measure channel informationbased on the reference signals associated with the subset of antennaports. The measured channel information is reported to the network node.

According to certain embodiments, a wireless device configured to beserved by a plurality of network nodes each comprising an antenna arrayis provided. The wireless device includes one or more processors. Theone or more processors are configured to, while being served by a firstnetwork node, receive a reference signal in a specific set of resourceelements from the first network node and transmit feedback informationto the first network node. The reference signal or the combination ofthe reference signal and the set of resource elements is indicative ofan identifier. The one or more processors are further configured to,while being served by a second network node distinct from the firstnetwork node, receive a reference signal in said specific resourceelement from the second network node and transmit feedback informationto the second network node. The reference signal or the combination ofthe reference signal and the set of resource elements is indicative ofan identifier, and the wireless device is configured to receive thereference signal with different beamforming from the first and secondnetwork nodes in spite of equality of the identifiers.

According to certain embodiments, a computer program product comprisinginstructions stored on non-transient computer-readable media which, whenexecuted by a processor, performs the acts of: selecting a subset from apredetermined set of P CSI-RS ports for receiving channel information,wherein each CSI-RS port corresponds to a combination of a set ofresource elements and an antenna port of an antenna array, thepredetermined set comprises a first number P₁ of CSI-RS ports with afirst polarization state and a second number P₂ of CSI-RS ports with asecond polarization state, the first and second polarization statesbeing distinct; and populating the subset with Q CSI-RS ports in suchmanner that the ratio of CSI-RS ports respectively having the. first andsecond polarization states is equal to the ratio of the first and secondnumbers.

According to certain embodiments, a computer program product comprisinginstructions stored on non-transient computer-readable media which, whenexecuted by a processor, performs the acts of: while being served by afirst network node, receiving a reference signal in a set of specificresource elements from the first network node and transmitting feedbackinformation to the first network node, wherein the reference signal orthe combination of the reference signal and the set of resource elementsis indicative of an identifier: and while being served by a secondnetwork node distinct from the first network node, receiving a referencesignal in said set of specific resource elements from the second networknode and transmitting feedback information to the second network node,wherein the reference signal or the combination of the reference signaland the set of resource elements is indicative of an identifier. Thereference signal is received with different beamforming from the firstand second network nodes in spite of equality of the identifiers.

According to certain embodiments, a computer program product comprisinginstructions stored on non-transient computer-readable media which, whenexecuted by a processor, performs the acts of: receiving, from a networknode, a CSI-RS setup comprising K CSI reference signal configurationseach with N CSI-RS ports and an antenna configuration of the networknode with P antenna ports, wherein the network node is equipped with P=8or P>8 antenna ports for transmitting signals to the wireless device;determining a subset of Q antenna ports from the P antenna ports;measuring channel information based on the reference signals associatedthe subset of antenna ports, and reporting the measured channelinformation to the network node. In particular, each CSI referencesignal configuration may have N CSI-RS ports and an antennaconfiguration of a serving cell of the network node.

Certain embodiments of the present disclosure may provide one or moretechnical advantages. As one example, certain embodiments mayadvantageously not require additional signaling for configuring CSI-RSports for periodic CSI reporting. As another example, legacy terminalscan be supported with the same eNB antenna array as FD-MIMO supportingterminals without additional CSI-RS overhead, since the ports used for afirst type of feedback is a subset of the ports used for a second typeof feedback. As yet another example, the codebooks, which are designedfor cross polarized antenna arrays where the first half of antenna portsare on one polarization and the second half of antenna ports are on adifferent polarization, can be used both for the first type and thesecond type of feedback.

Other advantages may be readily apparent to one having skill in the art.Certain embodiments may have none, some, or all of the recitedadvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed embodiments and theirfeatures and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates the basic LTE downlink physical resource,

FIG. 2 illustrates the LTE time-domain structure:

FIG. 3 illustrates an example downlink subframe;

FIG. 4 illustrates uplink L1/L2 control signaling transmission on PUCCH;

FIG. 5 illustrates an example of spatial multiplexing operation;

FIGS. 6A-6C illustrate resource element grids;

FIG. 7 illustrates an example of a two-dimensional antenna array ofcross-polarized antenna elements;

FIG. 8 illustrates the port numbering for P=8 antenna ports;

FIG. 9 is a block diagram illustrating an embodiment of a network, inaccordance with certain embodiments;

FIG. 10 is a block schematic of an exemplary network node, in accordancewith certain embodiments:

FIG. 11 is a flow diagram of a method in a network node, in accordancewith certain embodiments;

FIG. 12 shows an example of 16 ports CSI-RS port indexing withaggregation of two 8-port CSI-RS configurations, in accordance withcertain embodiments;

FIG. 13 illustrates another example having 12 ports CSI-RS port indexingwith aggregation of three 4-antenna-port CSI-RS configurations, inaccordance with certain embodiments;

FIG. 14 illustrates an example of a 16-port CSI-RS configuration withaggregation of 8 legacy two ports CSI-RS configurations, in accordancewith certain embodiments;

FIG. 15 illustrates legacy 8-port CSI-RS configurations, in accordancewith certain embodiments;

FIG. 16 illustrates the selected CSI-RS ports for the first type of CSIreporting, in accordance with certain embodiments:

FIG. 17 illustrates an example computer networking virtual apparatus forselecting and populating CSI-RS ports for receiving channel information,according to certain embodiments;

FIG. 18 illustrates an exemplary wireless device, in accordance withcertain embodiments;

FIG. 19 is a flow diagram of a method in a user equipment, in accordancewith certain embodiments;

FIG. 20 is a flow diagram of a method in a user equipment, in accordancewith certain embodiments;

FIG. 21 illustrates an example computer networking virtual apparatus forreporting channel information, according to certain embodiments, and

FIG. 22 is a block schematic of an exemplary radio network controller orcore network node, in accordance with certain embodiments.

DETAILED DESCRIPTION

In 3GPP Release 13, additional antenna ports are specified for CSIfeedback, and up to 16 ports can be supported. In future releases, evenmore ports may be supported (e.g., 37.) However, legacy (Release 12 orearlier) wireless devices support at most 8 ports CSI measurements.Accordingly, there is a need to support legacy terminals with networknodes having more than 8 CSI-RS ports in an efficient manner that doesnot increase CSI-RS overhead. More specifically, a problem is bow toselect a subset of the Release 13 CSI-RS ports for legacy wirelessdevices and still match to the legacy codebook design forcross-polarized antenna arrays. Even for Release 13 wireless devices, itis beneficial if fewer CSI-RS ports are used for periodic reporting, andthe full set of CSI-RS antenna ports is used for aperiodic reporting. Aproblem then exists with respect to how to select a subset of theconfigured full set of CSI-RS ports for CSI measurement and reporting.

The present disclosure contemplates various embodiments that may addressthese and other deficiencies. In the following description, we denotethe use of P>8 ports as the second type of CSI reporting (or feedback)and the use of Q≤8 ports as the first type of CSI reporting (orfeedback). The first type can thus be used for legacy terminal CSIreporting which do not support greater than 8 ports, or it can be usedfor PUCCH reporting for wireless devices of second type, e.g. Release13, (even if they support greater than 8 ports).

In certain embodiments, a first type of feedback and a second type offeedback may be defined where the first type uses Q≤8 ports and thesecond type is P>8 ports. The second type of feedback is arranged sothat First P/2 ports arc of one polarization, while the second half ofP/2 ports are of a different (orthogonal) polarization. Additionally,the CSI-RS resources used for the P ports are an aggregation of multipleCSI-RS configurations, each having N (N<P) ports.

The Q CSI-RS ports used for a first type of feedback is then chosen suchthat (either or both):

1. They have the same property (as described above) that the P>Q CSI-RSports used for the second type of feedback (i.e., the First Q/2 portsare with one polarization while the second half of Q/2 ports are with adifferent (orthogonal) polarization).

2. They occupy a subset or one of the aggregated CSI-RS configurationsused for defining or configuring ports of the second type of feedback.

In certain embodiments, a method for configuring a first set and asecond set of CSI-RS resources and the corresponding CSI-RS antennaports in a network is disclosed. The first set may have Q ports, and thesecond set may have P>Q ports. The second set may contain an aggregationof K CSI-RS configurations, each having N ports, such that P=NK. The P/2first ports are mapped to antennas of a first polarization, and the P/2last ports are mapped to antennas of a second polarization. A mapping ofthe P ports in the second set of resources to the N ports in each of theK CSI-RS configurations is established. Then, a mapping of ports in thefirst set of resources to ports in the second set of resources isestablished so that the Q/2 first ports are mapped to antennas of afirst polarization, and the Q/2 last ports are mapped to antennas of asecond polarization,

In some cases, the Q ports are mapped to the N ports of one of the Kconfigurations used for aggregating the second set of resources. Theports of the second set of resources may be numbered so that the P/2first ports are mapped to antennas of a first polarization, and the P/2last ports are mapped to antennas of a second polarization.

The various embodiments described herein may advantageously not requireadditional signaling for configuring CSI-RS ports for periodic CSIreporting. In addition, legacy terminals can be supported with the sameeNB antenna array as FD-MIMO supporting terminals without additionalCSI-RS overhead, since the ports used for first type of CSI feedback isa subset of the ports used for second type of CSI feedback. Furthermore,the codebooks, which are designed for cross polarized antenna arrayswhere the first half of antenna ports are of one polarization and thesecond half of antenna ports are of a different polarization, can beused both for the first type and the second type of feedback.

FIG. 9 is a block diagram illustrating an embodiment of a network 100,in accordance with certain embodiments Network 100 includes one or morewireless devices 110A-C, which may be interchangeably referred to aswireless devices 110 or UEs 110, and network nodes 115A-C, which may beinterchangeably referred to as network codes 115 or eNodeBs 115.Wireless devices 110 may communicate with network nodes 115 over awireless interface. For example, wireless device 110A may transmitwireless signals to one or more of network nodes 115, and/or receivewireless signals from one or more of network nodes 115. The wirelesssignals may contain voice traffic, data traffic, control signals, and/orany other suitable information. In some embodiments, an area of wirelesssignal coverage associated with a network node 115 may be referred to asa cell. In some embodiments, wireless devices 110 may have D2Dcapabilities. Thus, wireless devices 110 may be able to receive signalsfrom and/or transmit signals directly to another wireless device. Forexample, wireless device 110A may be able to receive signals from and/ortransmit signals to wireless device 110B.

In certain embodiments, network nodes 115 may interface with a radionetwork controller. The radio network controller may control networknodes 115 and may provide certain radio resource management functions,mobility management functions, and/or other suitable junctions. Incertain embodiments, the functions of the radio network controller maybe included in network node 115. The radio network controller mayinterface with a core network node. In certain embodiments, the radionetwork controller may interlace with the core network node via aninterconnecting network. The interconnecting network may refer to anyinterconnecting system capable of transmitting audio, video, signals,data, messages, or any combination of the preceding. The interconnectingnetwork may include all or a portion, of a public switched telephonenetwork (PSTN), a public or private data network, a local area network(LAN), a metropolitan area network (MAN), a wide area network (WAN), alocal regional, or global communication or computer network such as theInternet, a wireline or wireless network, an enterprise intranet, or anyother suitable communication link, including combinations thereof.

In some embodiments, tine core network node may manage the establishmentof communication sessions and various other functionalities for wirelessdevices 110. Wireless devices 110 may exchange certain signals with thecore network node using the non-access stratum layer. In non-accessstratum signaling, signals between wireless devices 110 and the corenetwork node may be transparently passed through the radio accessnetwork. In certain embodiments, network nodes 115 may interface withone or more network nodes over an internode interface. For example,network nodes 115A and 115B may interface over an X2 interface.

As described above, example embodiments of network 100 may include oneor more wireless devices 110, and one or more different types of networknodes capable of communicating (directly or indirectly) with wirelessdevices 110. Wireless device 110 may refer to any type of wirelessdevice communicating with a node and/or with another wireless device ina cellular or mobile communication system. Examples of wireless device110 include a mobile phone, a smart phone, a PDA (Personal DigitalAssistant), a portable computer (e.g., laptop, tablet), a sensor, amodem, a machine-type-communication (MTC) device/machine-to-machine(M2M) device, laptop embedded equipment (LEE), laptop mounted equipment(LME), USB dongles, a D2D capable device, or another device that canprovide wireless communication A wireless device 110 may also bereferred to as UE, a station (STA), a device, or a terminal in someembodiments. Also, in some embodiments, generic terminology, “radionetwork node” (or simply “network node”) is used It can be any kind ofnetwork node, which may comprise a Node B, base station (BS),multi-standard radio (MSR) radio node such as MSR BS, eNode B, networkcontroller, radio network controller (RNC), base station controller(BSC), relay donor node controlling relay, base transceiver station(BTS), access point (AP), transmission points, transmission nodes, RRU,RRH, nodes in distributed antenna system (DAS), core network node (e.g.MSC, MME etc.), O&M, OSS, SON, positioning node (e.g. E-SMLC), MDT, orany suitable network node. Example embodiments of wireless devices 110,network nodes 115, and other network nodes (such as radio networkcontroller or core network node) are described in more detail withreference to FIGS. 10, 18, and 22 , respectively.

Although FIG. 9 illustrates a particular arrangement of network 100, thepresent disclosure contemplates that the various embodiments describedherein may be applied to a variety of networks having any suitableconfiguration. Fox example, network 100 may include any suitable numberof wireless devices 110 and network nodes 115, as well as any additionalelements suitable to support communication between wireless devices orbetween a wireless device and another communication device (such as alandline telephone). Furthermore, although certain embodiments may bedescribed as implemented in a long term evolution (LTE) network, theembodiments may be implemented in any appropriate type oftelecommunication system supporting any suitable communication standardsand using any suitable components, and are applicable to any radioaccess technology (RAT) or multi-RAT systems in which the wirelessdevice receives and/or transmits signals (e.g., data). For example, thevarious embodiments described herein may be applicable to LTE,LTE-Advanced, UMTS, HSPA, GSM, cdma2000, WiMax, WiFi, another suitableradio access technology, or any suitable combination of one or moreradio access technologies. Although certain embodiments may he describedin the context of wireless transmissions in the downlink, the presentdisclosure contemplates that the various embodiments are equallyapplicable in the uplink.

FIG. 10 is a block schematic of an exemplary network node 115, inaccordance with certain embodiments. As described above, network node115 may be any type of radio network node or any network node thatcommunicates with a wireless device and/or with another network node.Examples of a network node 115 are provided above.

Network nodes 115 may be deployed throughout network 100 as a homogenousdeployment, heterogeneous deployment, or mixed deployment. A homogeneousdeployment may generally describe a deployment made up of the same (orsimilar) type of network nodes 115 and/or similar coverage and cellsizes and inter-site distances. A heterogeneous deployment may generallydescribe deployments using a variety of types of network nodes 115having different cell sizes, transmit powers, capacities, and inter-sitedistances. For example, a heterogeneous deployment may include aplurality of low-power nodes placed throughout a macro-cell layout.Mixed deployments may include a mix of homogenous portions andheterogeneous portions.

Network node 115 may include one or more of transceiver 1010, processor1020, memory 1030, and network, interface 1040. In some embodiments,transceiver 1010 facilitates transmitting wireless signals to andreceiving wireless signals from wireless device 110 (e.g., via anantenna), processor 1020 executes instructions to provide some or all ofthe functionality described above as being provided by a network node115, memory 1030 stores the instructions executed by processor 1020, andnetwork interface 1040 communicates signals to backend networkcomponents, such as a gateway, switch, router, Internet, Public SwitchedTelephone Network (PSTN), core network nodes or radio networkcontrollers 130, etc.

In certain embodiments, network node 115 may be capable of usingmulti-antenna techniques, and may be equipped with multiple antennas andcapable of supporting MIMO techniques. The one or more antennas may havecontrollable polarization. In other words, each element may have twoco-located sub elements with different polarizations (e.g., 90 degreeseparation as in cross-polarization), so that different sets ofbeamforming weights will give the emitted wave different polarization.

Processor 1020 may include any suitable combination of hardware andsoftware implemented in one or more modules to execute instructions andmanipulate data to perform some or all of the described functions ofnetwork node 115. In some embodiments, processor 1020 may include, forexample, one or more computers, one or more central processing units(CPUs), one or more microprocessors, one or more applications, and/orother logic.

Memory 1030 is generally operable to store instructions, such as acomputer program, software, an application including one or more oflogic, rules, algorithms, code, tables, etc. and/or other instructionscapable of being executed by a processor. Examples of memory 1030include computer memory (for example. Random Access Memory (RAM) or ReadOnly Memory (ROM)), mass storage media (for example, a hard disk),removable storage media (for example, a Compact Disk (CD) or a DigitalVideo Disk (DVD)), and/or or any other volatile or non-volatile,non-transitory computer-readable and/or computer-executable memorydevices that store information.

In some embodiments, network interface 1040 is communicatively coupledto processor 1020 and may refer to any suitable device operable toreceive input for network node 115, send output from network node 115,perform suitable processing of the input or output or both, communicateto other devices, or any combination of the preceding. Network interface1040 may include appropriate hardware (e.g.. port, modem, networkinterface card, etc.) and software, including protocol conversion anddata processing capabilities, to communicate through a network.

Other embodiments of network node 115 may include additional componentsbeyond those shown in FIG. 10 that may be responsible for providingcertain aspects of the radio network node's functionality, including anyof the functionality described above and/or any additional functionality(including any functionality necessary to support the solutionsdescribed above). The various different types of network nodes mayinclude components having the same physical hardware but configured(e.g., via programming) to support, different radio access technologies,or may represent partly or entirely different physical components.

In certain embodiments, network node 115 signals to a wireless device110 the port layout M₁×M₂, where M,(i=1,2) is the number of antennaports per polarization for dimension i, and a configuration of CSI-RSreference signals corresponding to a total of P=2 M₁×M₂) CSI-RS portsconsisting of an aggregation of K N-port CSI-RS configurations asfollows:

CSI-RS configuration with k=0: N CSI-RS ports

CSI-RS configuration with k=1: N CSI-RS ports

CSI-RS configuration with k=K−1: N CSI-RS ports,

where P=K*N and N ∈ {2,4,8}. Hence, network node 115 signals a list ofthese K CSI-RS configurations by RRC to wireless device 110.

FIG. 11 illustrates a flow diagram of a method 1100 in a network node115, in accordance with certain embodiments. The method begins at step1104 with the selection, by network node 115, of a subset from apredetermined set of P CSI-RS ports for receiving channel information.Each CSI-RS port may correspond to a combination of a set of resourceelements and an antenna port of an antenna array. The predetermined setcomprises a first number P of CSI-RS ports with a first polarizationstare and a second number P of CSI-RS ports with a second polarizationstate, where the first and second polarization states are distinct.

At step 1108, the subset is populated with Q CSI-RS ports in such mannerthat the ratio of CSI-RS ports respectively having the first and secondpolarization states is equal to the ratio of the first and secondnumbers. In certain embodiments, the subset may be populated withQP₁/(P₁+P₂) CSI-RS posts having the first polarization state andQP₂/(P₁+P₂) CSI-RS ports having the second polarization state. Incertain embodiments, P₁ and P₂ may be equal In certain embodiments, halfof the CSI-RS ports in the subset may have the first polarization stateand half of the CSI-RS ports in the subset have the second polarizationstate.

In a first particular embodiment, for example, the CSI measurement offirst type of report may be performed over the CSI-RS ports frommultiple, or all, of the aggregated CSI-RS configurations used in thesecond type of report. When numbering the antenna ports for the secondtype of reporting, having P>8 CSI-RS ports, then the followingexpression may be used:

$p = \left\{ \begin{matrix}{r + {\frac{N}{2}k}} & {{r = 15},16,\ldots\;,{14 + \frac{N}{2}}} \\{r + {\frac{N}{2}\left( {k + K - 1} \right)}} & {{r = {15 + \frac{N}{2}}},\ldots\;,{14 + N}}\end{matrix} \right.$where k (=0, . . . , K−1) correspond to the k-th component, of the KCSI-RS configurations (each having N antenna ports) and r is the portindex of each component CSI-RS configuration, Each CSI-RS port in thepredetermined set may be associated with an identifier selected from anordered set. The first number P1 of CSI-RS ports may be associated withidentifiers in a first predetermined range and a second number P2 ofCSI-RS ports may be associated with identifiers in a secondpredetermined range. The subset may be populated with a number of CSI-RSports from a lower portion of the first predetermined range and an equalnumber of CSI-Reports from a lower portion of the second predeterminedrange, in a particular embodiment. However, it is may be recognized thatthe subset may also be populated with a number of ports from an upperportion of each predetermined range, a mid portion of each predeterminedrange, a lower portion of each predetermined range, or any combinationthereof of the predetermined ranges. Such port numbering can also besummarized in Table 1 below for (N,K)=(8,2), (4,3) and Table 2 below for(N,K)=(2,8), (2,6).

TABLE 1 Mapping of 12 and 16 CSI-RS ports using aggregation of multipleeight (N = 8) and four (N = 4) ports CSI-RS configurations Port number(p) 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Port number of eachK = 2, Aggregated 0 15 16 17 18 — — — — 19 20 21 22 — — — — componentCSI-RS N = 8 configuration (k) 1 — — — — 15 16 17 18 — — — — 19 20 21 22configuration (r) K = 3, Aggregated 0 15 16 — — — — — — 17 18 — — — — —— N = 4 configuration (k) 1 — — 15 16 — — — — — — 17 18 — — — — 2 — — —— 15 16 — — — — — — 17 18 — —

TABLE 2 Mapping of 12 and 16 CSI-RS ports using aggregation of eight (K= 8) and six (K = 6) 2-port (N = 2) CSI-RS confiurations AggregatedCSI-RS Configuration (k) 0 1 2 3 4 5 6 7 Port number of each componentCSI-RS configuration (r) 15 16 15 16 15 16 15 16 15 16 15 16 15 16 15 16CSI-RS K = 8, N = 2 15 23 16 24 17 25 18 26 19 27 20 28 21 29 22 30 Portnumber K = 6, N = 2 15 21 16 22 17 23 18 24 19 25 20 26 — — — — (p)

In a particular embodiment, each CSI-RS port in the predetermined setmay be associated with an identifier selected from an ordered set. Thefirst number P1 of CSI-RS ports may be associated with identifiers in afirst predetermined range and a second number P2 of CSI-RS ports may beassociated with 10 identifiers in a second predetermined range.

FIG. 12 shows an example of 16 ports CSI-RS port indexing withaggregation of two 8-port CSI-RS configurations (i.e., N=8, K=2):configuration #0 (k=0) and configuration #1 (k=1). For example, if N=8,K=2, P=16, then the CSI-RS ports for the k=0 configuration are numberedas {15,16,17,18,23,24,25,26} and the ports for the k=1 configuration arenumbered as 15 {19,20,21.22,27,28,29,30} as shown in FIG. 12 . Now, theports 15-22 are mapped to antennas of the first polarization and 23-30to antennas of the second polarization. Hence, in this embodiment, eachof the K CSI-RS configurations are mapped to cross-polarized antennaswherein the first half of ports (i.e., ports 15 to 22) are mapped to onepolarization and the second half (i.e., ports 23 to 30) to the alternatepolarization. The CSI-RS signals on adjacent OFDM symbols are actuallycode division multiplexed with a length 2 Orthogonal Cover Code (OCC).For simplicity of illustration, only a single port number is labelled ineach RE in FIG. 12 . For example, the CSI-RS signals of ports 15 and 16are transmitted on both OFDM symbols 5 and 6 in slot 0. In addition,only the first resource block (RB) is shown, the same mapping alsoapplies to other RBs in the whole system bandwidth of a network node.

FIG. 13 illustrates another example having 12 ports CSI-RS port indexingwith aggregation of three 4-antenna-port CSI-RS configurations:configurations #0 (k=0), #1 (k=1) and #2 (k=2). The example illustratedin FIG. 13 includes 12 CSI-RS ports configured with aggregation withthree 4-antenna-port CSI-RS configurations (i.e., N=4, K=3). Again, eachof the K CSI-RS configurations are mapped to cross-polarized antennaswherein the first half of ports (i.e., ports 15 to 29) are mapped to onepolarization and the second half (i.e., ports 21 to 26) to the alternatepolarization.

Since legacy wireless devices, or PUCCH for Release 13 wireless devices(i.e., first type of feedback), need to map to Q ports where Q/2 firstports are co-polarized, and last Q/2 ports also are co-polarized (butwith orthogonal polarization) among the P>Q ports used for second typeof feedback, the first type of feedback using Q antenna ports can selectthe first configuration (i.e., k=0) (or the second configuration) in theexample shown in FIG. 12 for Q=8 and FIG. 13 for Q=4 and then the goalis directly achieved.

In certain embodiments, some generalized port numbering rules may beemployed to achieve this objective for more general values of{M1,M2,P,Q,N,K} than what was assumed in the example described above.For example, the number of CSI-RS ports, Q ∈ {2,4,8}, used for legacywireless devices 110 (that only support at most 8 ports) and for Release13 wireless devices 110 using periodic CSI measurement and report onPUCCH may be determined by the following rule: Q=min(4└max(M₁,M₂)/2┘,8). The Q CSI-RS ports for first type of reporting can then beselected from the ports defined for the second type of reporting asfollows:

$\left\{ {15,16,\ldots\;,{14 + \frac{Q}{2}},{15 + \frac{P}{2}},\ldots\;,{14 + \frac{P}{2} + \frac{Q}{2}}} \right\}$Some examples of Q CSI-RS port numbering for first type of reporting areshown in Table 3 below.

TABLE 3 Examples of CSI-RS ports used for P-CSI measurement and report:linking Q to the size of 2D antenna array Subset of CSI-RS ports forfirst type of reporting among ports used for Port numbering for first M₁M₂ P Q second type of reporting type of reporting 8 1 16 8 15, 16, 17,18, 23, 24, 25, 26 15, 16, 17, 18, 19, 20, 21, 22 6 1 12 8 15, 16, 17,18, 21, 22, 23, 24 15, 16, 17, 18, 19, 20, 21, 22 4 2 16 8 15, 16, 17,18, 23, 24, 25, 26 15, 16, 17, 18, 19, 20, 21, 22 2 4 16 8 15, 16, 17,18, 23, 24, 25, 26 15, 16, 17, 18, 19, 20, 21, 22 3 2 12 4 15, 16, 21,22 15, 16, 17, 18 2 3 12 4 15, 16, 21, 22 15, 16, 17, 18

For instance, if M1=2 and M2=3, and Q=4 ports are used for the firsttype of CSI reporting and P=12 ports are used for second type ofreporting, then ports 15-20 in the second type of reporting will useco-polarized antennas with one polarization, while ports 21-26 will alsobe a set of co-polarized antennas, but with orthogonal polarization withrespect to ports 15-20. For the first type of reporting, the four ports15-16 and 21-22 are selected among the ports used for second type ofreporting. These ports are then re-numbered for the first type ofreporting as ports 15-18 respectively to achieve the desired goal thatthe first Q/2 ports are co-polarized and the last Q/2 ports are alsoco-polarized but with alternative polarization.

However, the Q CSI-RS ports defined in this way may not alwayscorrespond to a resource mapping that exists for a CSI resource of Qports among the legacy CSI-RS resources For example, FIG. 14 illustratesan example of a 16-port CSI-RS configuration with aggregation, of 8legacy 2-port CSI-RS configurations (i.e., N=2, K=8), in accordance withcertain embodiments. By contrast, FIG. 15 illustrates legacy 8-portCSI-RS configurations, in accordance with certain embodiments. If K=8,N=2 CSI resource of the second type is configured for 16 ports as shownin FIG. 14 , and Q=8 ports is desired for the first type of resourceaggregation of arbitrary four 2-port CSI-RS configurations may not havethe same resource as that of the legacy 8 ports CSI-RS shown in FIG. 15. Therefore, this embodiment is useful for periodic CSI reporting by newRel-13 wireless devices 110 but not necessarily for legacy wirelessdevices that are not aware of the new design. If this is desirable, thenthe solution in embodiment 2 can be applied.

FIG. 16 illustrates the selected CSI-RS ports for the first type of CSIreporting, in accordance with certain embodiments. More particularly,FIG. 16 illustrates the selected CSI-RS ports for P-CSI reporting inease of 2*4 and 4×2 antenna port layout (i.e., M1×M2).

In the first particular embodiment described above, CSI measurement of afirst type of report was performed over the CSI-RS ports from multiple,or all, of the aggregated CSI-RS resources used in the second type ofreport. According to a second particular embodiment, the ports relatedto the first type are confined to a single CSI-RS configuration of themultiple aggregated configurations configured for the second type of CSImeasurement, and resource. When numbering the antenna ports for thesecond type of reporting, having P>8 CSI-RS ports, then the followingexpression is used:

$p = \left\{ \begin{matrix}{r + {\frac{N}{2}k}} & {{r = 15},16,\ldots\;,{14 + \frac{N}{2}}} \\{r + {\frac{N}{2}\left( {k + K - 1} \right)}} & {{r = {15 + \frac{N}{2}}},\ldots\;,{14 + N}}\end{matrix} \right.$where k (=0, . . . , K−1) correspond to the k-th CSI-RS configuration(each having N ports). This is the same as that in the first embodiment,and each of the K CSI-RS configurations are mapped to cross-polarizedantennas wherein the first half of ports are mapped to one polarizationand the second half to the alternate polarization

For example, if N=8, K=2, P=16, then the ports for the k=0 configurationare numbered as {15,16,17,18,23,24,25,26}. Now, the ports 15-22 aremapped to antennas of tire first polarization and ports 23-30 are mappedto antennas of the second polarization.

Again, since CSI report of the first type such as legacy wirelessdevices 110, or PUCCH for Release 13 wireless devices 110, need to mapto Q ports where Q/2 first ports are co-polarized, and last Q/2 portsalso are co-polarized (but with orthogonal polarization), the followingport selection for the first type of CSI report is proposed in thisembodiment to use the first (i.e., k=0) N CSI-RS ports for measurementsand reports of the first type (i.e., Q=N). Or alternatively, to use apredefined configuration (e.g., k=0 or k=1) of the K configurationsassigned to the second type of reporting, for measurements and reportsof the first type.

In comparison, to the first particular embodiment described above, thenumber of ports of the first type can be changed depending on the valueN used per aggregated configuration in the configuration of the secondtype. More importantly, the ports of the first type have the same CSI-RSresource as that for a legacy CSI-RS configuration with N ports, andthese N ports from a single resource contain a complete set ofcross-polarized antennas as legacy N ports. Therefore, a legacy wirelessdevice 110 can be configured with Q=N CSI-RS ports and perform CSImeasurement and report according to pre-Release 13 procedures. A Release13 wireless device 110 can also perform periodic CSI measurement andreport with the selected Q CSI-RS ports according to pre-Release 13procedures.

An example of the subset of CSI-RS ports selected in this embodiment forCSI reporting of the first type and/or for CSI reporting by a legacywireless device 110 is shown in Table 4 below.

TABLE 4 Examples of CSI-RS ports used for P-CSI measurement and report:M = N Subset of CSI-RS ports for first type of reporting among portsused Port numbering for first M₁ M₂ P N K Q for second type of reportingtype of reporting 8 1 16 8 2 8 15, 16, 17, 18, 23, 24, 25, 26 15, 16,17, 18, 19, 20, 21, 22 6 1 12 4 3 4 15, 16, 21, 22 15, 16, 17, 18 4 2 168 2 8 15, 16, 17, 18, 23, 24, 25, 26 15, 16, 17, 18, 19, 20, 21, 22 2 416 2 8 2 15, 23 15, 16 3 2 12 4 3 4 15, 16, 21, 22 15, 16, 17, 18 2 3 122 6 2 15, 21 15, 16

In certain embodiments, the method for selecting and populating CSI-RSports for receiving channel information as described above may beperformed by a computer networking virtual apparatus. FIG. 17illustrates an example computer networking virtual apparatus 1700 forselecting and populating CSI-RS ports for receiving channel information,according to certain embodiments. In certain embodiments, virtualcomputing device 1700 may include modules for performing steps similarto those described above with regard to the method illustrated anddescribed in FIG. 11 . For example, computer networking virtualapparatus 1700 may include a selecting module 1710, a populating module1720, and any other suitable modules for selecting and populating CSI-RSports for receiving channel information In some embodiments, one or moreof the modules may be implemented using one or more processors 1020 ofFIG. 10 . In certain embodiments, the functions of two or more of thevarious modules may be combined into a single module.

The selecting module 1710 may perform the selecting functions ofcomputer networking virtual apparatus 1700. For example, selectingmodule 1710 may select a subset from a predetermined set of P CSI-RSports for receiving channel information. Each CSI-RS port may correspondto a combination of a set of resource elements and an antenna port of anantenna array. The predetermined set may include a first number P₁ ofCSI-RS ports with a first polarization state and a second number P₂ ofCSI-RS ports with a second polarization state, where the first andsecond polarization states are distinct, in certain embodiments.

The populating module 1720 may perform the populating functions ofcomputer networking virtual apparatus 1700. For example, populatingmodule 1720 may populate the subset with Q CSI-RS ports m such mannerthat the ratio of CSI-RS ports respectively having the first and secondpolarization states is equal to the ratio of the first and secondnumbers. In certain embodiments, the subset may be populated withQP₁/(P₁+P₂) CSI-RS ports having the first polarization state andQP₂/(P₁+P₂) CSI-RS ports having the second polarization state. Incertain embodiments, P₁ and P₂ may be equal. In certain embodiments,half of the CSI-RS ports in the subset may have the first polarizationstate and half of the CSI-RS ports in the subset have the secondpolarization state.

Other embodiments of computer networking virtual apparatus 1700 mayinclude additional components beyond those shown in FIG. 17 that may beresponsible for providing certain aspects of the functionality ofnetwork node 115, including any of the functionality described aboveand/or any additional functionality (including any functionalitynecessary to support the solutions described above). The variousdifferent types of network nodes 115 may include components having thesame physical hardware but configured (e.g., via programming) to supportdifferent radio access technologies, or may represent partly or entirelydifferent physical components.

FIG. 18 is a block schematic of an exemplary wireless device 110, inaccordance with certain embodiments. Wireless device 110 may refer toany type of wireless device communicating with a node and/or withanother wireless device in a cellular or mobile communication system. Asdepicted, wireless device 110 includes transceiver 1810, processor 1820,and memory 1830. In some embodiments, transceiver 1810 facilitatestransmitting wireless signals to and receiving wireless signals fromnetwork node 115 (e.g., via an antenna), processor 1820 executesinstructions to provide some or all of the functionality described aboveas being provided by wireless device 110, and memory 1830 stores theinstructions executed by processor 1820. Examples of a network node 115are provided above.

Processor 1820 may include any suitable combination of hardware andsoftware implemented in one or more modules to execute instructions andmanipulate data to perform some or all of the described functions ofwireless device 110. In some embodiments, processor 1820 may include,for example, one or more computers, one or more central processing units(CPUs), one or more microprocessors, one or more applications, and/orother logic.

Memory 1830 is generally operable to store instructions, such as acomputer program, software, an application including one or more oflogic, roles, algorithms, code, tables, etc. and/or other instructionscapable of being executed by a processor. Examples of memory 1830include computer memory (for example, Random Access Memory (RAM) or ReadOnly Memory (ROM)), mass storage media (for example, a hard disk),removable storage media (for example, a Compact Disk (CD) or a DigitalVideo Disk (DVD)), and/or or any other volatile or non-volatile,non-transitory computer-readable and/or computer-executable memorydevices that store information.

Other embodiments of wireless device 110 may include additionalcomponents beyond those shown in FIG. 18 that may be responsible forproviding certain aspects of tire wireless device's functionality,including any of the functionality described above and/or any additionalfunctionality (including any functionality necessary to support thesolution described above).

FIG. 19 is a flow diagram of a method in a wireless device 110, inaccordance with certain embodiments. In certain embodiments, wirelessdevice 110 is served by a network node 115 equipped with more than,eight antenna ports for transmitting signals to wireless device 110within a wireless communication network. The method begins at step 1904,when wireless device 110 receives a CSI-RS setup from network node 115.The CSI-RS setup comprises K CSI-RS configurations each with N (legacy)CSI-RS ports and an antenna configuration of the network node with Pantenna ports. In a particular embodiment, for example, the antennaconfiguration includes P CSI-RS ports.

At step 1908, wireless device 110 determines a subset of Q antenna portsfrom the P antenna ports. In a particular embodiment, for example, afirst subset of P/2 CSI-RS ports and a second subset of P/2 CSI-RS portsmay be determined from the P CSI-RS ports. The first subset may includeN/2 CSI-RS ports from each of the K CSI-RS configurations, and thesecond subset may include the remaining N/2 CSI-RS ports from each ofthe K CSI-RS configurations. In a particular embodiment, the firstsubset may correspond to a first length-P/2 vector of a length-Ppreceding vector in. a codebook used for state information feedback. Bycontrast the second subset may correspond to a second length-P/2 vectorof the same length-P precoding vector, wherein the second length-P/2vector is obtainable by scaling the first length-P/2 vector by a complexnumber.

In certain embodiments, determining the subset of Q antenna ports fromthe P antenna ports at step 1908 may include forming the first subset asCSI-RS ports indexed by

${p = {{r + {\frac{N}{2}k\mspace{14mu} r}} = 15}},16,\ldots\;,{14 + \frac{N}{2}},$Conversely, the second subset may be formed as CSI-RS ports indexed by

${{p = {r + {\frac{N}{2}\left( {k + K - 1} \right)}}};{r = {15 + \frac{N}{2}}}},\ldots\;,{14 + {N.}}$In both subsets, k may run over the K CSI-RS configuration, k=0, 1, . .. , K−1.

At step 1912, wireless device 110 measures channel information based onthe reference signals associated with the subset of antenna ports. Forexample, the channel information may be estimated over receivedreference signals associated with the subset of ports based on apredefined codebook of Q ports, in a particular embodiment.Additionally, the measuring of channel information may be performedperiodically, in certain embodiments.

At step 1916, wireless device 110 reports the measured channelinformation to the network node 115. For example, estimated channelinformation may be sent to the network node 115 over a regular physicaluplink control channel, in a particular embodiment. Additionally, thereporting of channel information may be performed periodically, incertain embodiments.

FIG. 20 is a flow diagram of a method 2000 in a wireless device 110, inaccordance with certain embodiments. The method begins at step 2004,when, while being served by a first network node 115, a wireless device110 receives a reference signal in a specific set of resource elementsfrom the first network node 115 and transmits feedback information tothe first network node 115, wherein the reference signal or thecombination of the reference signal and the set of resource elements isindicative of an identifier.

At step 2008, while being served by a second network node 115 distinctfrom the first network node 115, wireless device 110 receives areference signal in said specific set of resource elements front thesecond network node 115 and transmits feedback information to the secondnetwork node 115. The reference signal or the combination of thereference signal and the set of resource elements is indicative of anidentifier.

In certain embodiments, the method for providing channel information asdescribed above may be performed by a computer networking virtualapparatus, FIG. 21 illustrates an example computer networking virtualapparatus 2100 for providing channel information, according to certainembodiments. In certain embodiments, virtual computing device 2100 mayinclude modules for performing steps similar to those described abovewith regard to the methods illustrated and described in FIGS. 19 and 20. For example, computer networking virtual apparatus 2100 may include areceiving module 2110, a determining module 2120, a measuring module2130, a transmitting and/or reporting module 2140, and any othersuitable modules for providing channel information. In some embodiments,one or more of the modules may be implemented using one or moreprocessors 1820 of FIG. 18 . In certain embodiments, the functions oftwo or more of the various modules may be combined into a single module.

The receiving module 2110 may perform the receiving functions ofcomputer networking virtual apparatus 2100. For example, in certainembodiments, receiving module 2110 may receive a CSI-RS setup from anetwork node. The CSI-RS setup may include K-CSI-RS configurations, eachwith N CSI-RS ports and an antenna configuration of the network nodewith P antenna ports.

As another example, in certain embodiments, receiving module 2110 mayreceive a reference signal in a specific set of resource elements fromthe first network node 115. The reference signal from the first networknode or the combination of the reference signal and the set of resourceelements are indicative of an identifier. Receiving module 2110 may alsoreceive a reference signal in said set of specific resource elementsfrom a second network node while being served by the second network node115. Likewise, the reference signal from the second network node or thecombination of the reference signal and the set of resource elements arealso indicative of an identifier. The reference signals may be receivedwith different, beamforming in spite of tire equality of theidentifiers.

The determining module 2120 may perform the determining functions ofcomputer networking virtual apparatus 2100. For example, determiningmodule 2100 may determine a subset of Q antenna ports from the P antennaports received by receiving module 2110 in certain embodiments.

The measuring module 2130 may perform the measuring functions ofcomputer networking virtual apparatus 2100. For example, measuringmodule 2130 may measure channel information based on the referencesignals associated with the subset of antenna ports. In a particularembodiment, the measuring module 2130 may perform the measuringperiodically.

The transmitting and/or reporting module 2140 may perform thetransmitting and/or reporting functions of computer networking virtualapparatus 2100. For example, in certain embodiments, transmitting and/orrepotting module 2140 may report the measured channel information to thenetwork node. In a particular embodiment, the transmitting and/orreporting module 2140 may perform the reporting function periodically.

In certain embodiments, transmitting and/or reporting module 2140 maytransmit feedback information to the first network node 115.Additionally or alternatively, transmitting and/or reporting module 2140may transmit feedback information to the second network node 115.

Other embodiments of computer networking virtual apparatus 2100 mayinclude additional components beyond those shown in FIG. 21 that may beresponsible for providing certain aspects of the wireless device's 110functionality, including any of the functionality described above and/orany additional functionality (including any functionality necessary tosupport the solutions described above). The various different types ofwireless devices 110 may include components having the same physicalhardware but configured (e.g., via programming) to support differentradio access technologies, or may represent partly or entirely differentphysical components.

FIG. 22 is a block schematic of an exemplary radio network controller orcore network node 130 in accordance with certain embodiments. Examplesof network nodes can include a mobile switching center (MSC), a servingGPRS support node (SGSN), a mobility management entity (MME), a radionetwork controller (RNC), a base station controller (BSC), and so on.The radio network controller or core network node 130 include processor2220, memory 2239, and network interface 2240. In some embodiments,processor 2220 executes instructions to provide some or all of thefunctionality described above as being provided by the network node,memory 2230 stores the instructions executed by processor 2220, andnetwork interface 2240 communicates signals to any suitable node, such,as a gateway, switch, router, Internet, Public Switched TelephoneNetwork (PSTN), network nodes 115, radio network controllers or corenetwork nodes 130, etc.

Processor 2220 may include any suitable combination of hardware andsoftware implemented in one or more modules to execute instructions andmanipulate data to perform some or all of the described functions of theradio network controller or core network node 130. In some embodiments,processor 2220 may include, for example, one or more computers, one ormore central processing units (CPUs), one or more microprocessors, oneor more applications, and/or other logic.

Memory 2230 is generally operable to store instructions, such as acomputer program, software, an application including one or more oflogic, rules, algorithms, code, tables, etc. and/or other instructionscapable of being executed by a processor. Examples of memory 2230include computer memory (for example. Random Access Memory (RAM) or ReadOnly Memory (ROM)), mass storage media (for example, a hard disk),removable storage media (for example, a Compact Disk (CD) or a DigitalVideo Disk (DVD)), and/or or any other volatile or non-volatile,non-transitory computer-readable and/or computer-executable memorydevices that store information.

In some embodiments, network interface 2240 is communicatively coupledto processor 2220 and may refer to any suitable device operable toreceive input for the network node, send output from tire network node,perform suitable processing of The input or output or both, communicateto other devices, or any combination of the preceding. Network interface2240 may include appropriate hardware (e.g., port, modem, networkinterface card, etc.) and software, including protocol conversion anddata processing capabilities, to communicate through a network.

Other embodiments of the network node may include additional componentsbeyond those shown in FIG. 22 that may be responsible for providingcertain aspects of the network node's functionality, including any ofthe functionality described above and/or any additional functionality(including any functionality accessary to support the solution describedabove).

According to certain embodiments, a method of selecting a subset from apredetermined set of P CSI-RS ports for receiving channel stateinformation is provided. The method is implemented in a network node(115) of a wireless communication network (100). The network nodecomprises an antenna array with controllable polarization. Each CSI-RSport corresponds to a combination of a set of resource elements and anantenna port of said antenna array. The predetermined set comprises afirst number P₁ of CSI-RS ports with a first polarization state and asecond number P₂ of CSI-RS ports with a second polarization state, wherethe first and second polarization states distinct. The method includespopulating the subset with Q CSI-RS ports in such manner that the ratioof CSI-RS ports respectively having the first and second polarizationstates is equal to the ratio of the first and second numbers.

Optionally, The subset is populated with QP₁/(P₁+P₂) CSI-RS ports havingthe first polarization state and QP₂/(P₁+P₂) CSI-RS ports having thesecond polarization state.

Optionally, P₁=P₂, whereby the subset is populated with equalproportions of CSI-RS ports with the first and second polarizationstates.

Optionally, P₁+P₂=P.

Optionally, half of the CSI-RS ports in the subset have the firstpolarization state and half of the CSI-RS ports in the subset have thesecond polarization state.

Optionally, Q≤X.

Optionally, Q is a multiple of 2.

Optionally, Q=2 or Q=4 or Q=8.

Optionally, each CSI-RS port in the predetermined set is associated withan identifier susceptible of enabling the network node to identifyfeedback relating to a reference signal transmitted by the network nodeon this CSI-RS port.

Optionally, one of the following holds: the identifier is explicitlystated in a feedback signal; the identifier is implicitly derivable froman internal structure of a feedback signal; and the identifier isimplicitly derivable from a resource used for transmitting a feedbacksignal.

Optionally, the CSI-RS ports are selected from an ordered set.

Optionally, the ordered set is one of a subset of the integers or asubset of an alphabet.

Optionally, populating the subset includes preserving the identifierswith which the CSI-RS ports are associated.

Optionally, the CSI-RS ports with a first polarization state areassociated with identifiers in a first predetermined range, and theCSI-RS ports with a second polarization state are associated withidentifiers in a second predetermined range. The subset is populatedwith Q/2 CSI-RS ports from a lower portion of the first predeterminedrange and Q/2 CSI-RS ports from a lower portion of the secondpredetermined range.

Optionally, each CSI-RS port is associated with an identifier being aport number p given by

$p = \left\{ \begin{matrix}{r + {\frac{N}{2}k}} & {{r = 15},16,\ldots\;,{14 + \frac{N}{2}}} \\{r + {\frac{N}{2}\left( {k + K - 1} \right)}} & {{r = {15 + \frac{N}{2}}},\ldots\;,{14 + N}}\end{matrix} \right.$where K is a number of CSI reference signal configurations, k is anyinteger in [0, K−1], N is the number of antenna ports or referencesignals in each of the K configurations, and r is any integer in[15,14+N].

Optionally, the subset is populated with Q CSI-RS ports associated withport numbers given by

$p = \left\{ \begin{matrix}{r + {\frac{N}{2}k}} & {{r = 15},16,\ldots\;,{14 + \frac{N}{2}}} \\{r + {\frac{N}{2}\left( {k + K - 1} \right)}} & {{r = {15 + \frac{N}{2}}},\ldots\;,{14 + N}}\end{matrix} \right.$where k is restricted to

$\left\lbrack {0,{\frac{Q}{N} - 1}} \right\rbrack$and Q≥N.

Optionally, the CSI-RS ports are associated with alternativeidentifiers, which are selected from the ordered set and susceptible ofenabling the network node to identify a first type of feedback relatingto a CSI reference signal transmitted by the network node on a CSI-RSport.

Optionally, the identifiers define an ordering of the CSI-RS ports,which is preserved by the alternative identifiers.

Optionally, the alternative identifiers are consecutive.

Optionally, the alternate identifiers p′ are given by

$p^{\prime} = \left\{ \begin{matrix}{{p,}\mspace{121mu}} & {{q = 0};} \\{{p - \frac{{KN} - Q}{2}},} & {q = 1.}\end{matrix} \right.$where q=0 is for the first polarization state and q=1 is for the secondpolarization state.

Optionally, an aggregated resource and port number are assigned to eachCSI-RS port in the subset.

Optionally, the number Q of CSI-RS ports in the subset is determined asa function of the number P of CSI-RS ports in the predetermined set.

Optionally, determining includes one of: selecting Q≤8 such that Q<P;selecting Q ∈ {2,4,8} such that Q<P: selecting a greatest possible Q≤8such that Q<P; and selecting a greatest possible Q ∈ {2,4,8} such thatQ<P.

Optionally, the method is implemented in a network node comprising anantenna array with antenna elements arranged along two axes.

Optionally, the first polarization state corresponds to a linear arrayof antenna elements with one polarization direction and the secondpolarization state corresponds to a linear array of antenna elementswith a second polarization direction.

Optionally, the antenna array comprises cross-polarized antennaelements.

Optionally, the method further includes transmitting a plurality of CSIreference signals over CSI-RS ports from the predetermined set andreceiving feedback from, a user equipment (110) in the wirelesscommunication network.

Optionally, the method further includes determining whether feedback ofa first or second type is to be enabled. If feedback of the first typeis to be enabled, transmitting reference signals on CSI-RS ports fromthe subset. If feedback of the second type is to be enabled,transmitting reference signals on CSI-RS ports from the predeterminedset.

Optionally, the method further includes using a common codebook for bothtypes of reporting.

Optionally, the method further includes using a first codebook for thefirst type of reporting and a second codebook for the second type ofreporting.

Optionally, the first type of feedback is periodic CSI reporting,

Optionally, the method further includes an initial step of signaling tothe user equipment a number P of antenna ports by which the network nodeis configured and signaling a configuration of CSI-RS portscorresponding to the total of P CSI-RS ports being K aggregated N-portCSI-RS configurations, where K is the number of available CSI referencesignal configurations.

According to certain embodiments, a method in a user equipment (110)operable in a wireless communication network (100), operable to beserved by a plurality of network nodes (115), each of which comprises anantenna, array is provided. The method includes, while being served by afirst network node (115A), receiving a reference signal in a specificset of resource elements from the first network node and transmittingfeedback information to the first network node. The reference signal orthe combination of the reference signal and the set of resource elementsis indicative of an identifier. While being served by a second networknode (115B) distinct from the first network node, a reference signal insaid, set of specific resource elements is received from the secondnetwork node, and feedback information is transmitted to the secondnetwork node. The reference signal or the combination of the referencesignal and the set of resource elements is indicative of an identifier,wherein the reference signal is received with different beamforming fromthe first and second network nodes in spite of equality of theidentifiers.

According to certain embodiments, a method in a user equipment (110) isserved by a wireless communication network node (115) equipped with morethan eight antenna ports for transmitting signals to the UE. The methodincludes receiving, from the network node, a CSI-RS configurationcomprising K CSI-RS configurations each with N CSI-RS ports and anantenna configuration of the network node with P antenna ports. A subsetof Q antenna ports is determined from the P antenna ports. Channel stateinformation is periodically measured based on the reference signalsassociated the subset of antenna ports. The measured channel stateinformation is periodically reported to the network node.

According to certain embodiments, a method in a network node isdisclosed. The method comprises selecting a subset front a.predetermined set of P CSI-RS ports for receiving channel information.The network node comprises an antenna army with controllablepolarization. Each CSI-RS port corresponds to a combination of a set ofresource elements and an antenna port of said antenna array. Thepredetermined set comprises a first number P₁ of CSI-RS ports with afirst polarization state and a second number P₂ of CSI-RS ports with asecond polarization state. The first and second polarization states aredistinct. The method further comprises populating the subset with QCSI-RS ports in such manner that the ratio of CSI-RS ports respectivelyhaving the first and second polarization states is equal to the ratio ofthe first and second numbers.

According to certain embodiments, a method in a wireless device servedby a network node of a wireless communication network is provided. Thenetwork node is equipped with P=8 or P>8 antenna ports for transmittingsignals to the wireless device. The method includes receiving, from thenetwork node, a CSI-RS setup that includes K CSI-RS configurations eachwith N CSI-RS ports and art antenna configuration of the network nodewith P antenna ports. A subset of Q antenna ports is determined from theP antenna ports. Channel information is measured based on the referencesignals associated with the subset of antenna ports The measure channelinformation is reported to the network node.

According to certain embodiments, a method in a wireless device of awireless communication network is provided. The wireless device isserved by a plurality of network nodes, and each network node includesan antenna array. The method includes receiving a reference signal in aspecific set of resource elements from a first network node while beingserved by the first network node. Feedback information is transmitted tothe first network node. The reference signal or the combination of thereference signal and the set of resource elements is indicative of anidentifier. While being served by a second network node distinct fromthe first network node, a reference signal in said set of specificresource elements is received from the second network node. Feedbackinformation is transmitted to the second network node, and the referencesignal or the combination of the reference signal and the set ofresource elements is indicative of an identifier. The reference signalis received with different beamforming from the first and second networknodes in spite of the equality of the identifiers.

According to certain embodiments, a network node is provided. Thenetwork node includes an antenna array with controllable polarization,and one or more processors. The one or more processors are configured toselect a subset from a predetermined set of P CSI-RS ports for receivingchannel information, wherein each CSI-RS port corresponds to acombination of a set of resource elements and an antenna port of saidantenna array, the predetermined set comprises a first number P₁ ofCSI-RS ports with a first polarization state and a second number P₂ ofCSI-RS ports with a second polarization state, the first and secondpolarization states being distinct. The one or more processors arefurther configured to populate the subset with Q CSI-RS ports in suchmanner that the ratio of CSI-RS ports respectively having the first andsecond polarization states is equal to the ratio of the first and secondnumbers

According to certain embodiments, a wireless device configured to beserved by a network node in a wireless communication network isprovided. The network node is equipped with P=8 or P>8 antenna ports fortransmitting signals to the wireless device. The wireless deviceincludes one or more processors. The one or more processors areconfigured to receive, from the network node, a CSI-RS set up comprisingK CSI reference signal configurations each with N CSI-RS ports and anantenna configuration of the network node with P antenna ports. The oneor more processors are further configured to determine a subset of Qantenna ports from the P antenna ports and measure channel informationbased on the reference signals associated with the subset of antennaports. The measured channel information is reported to the network node.

According to certain embodiments, a wireless device configured to beserved by a plurality of network nodes each comprising an antenna arrayis provided. The wireless device includes one or more processors. Theone or more processors axe configured to, while being served by a firstnetwork node, receive a reference signal in a specific set of resourceelements from the first network node and transmit feedback informationto the first network node. The reference signal or the combination ofthe reference t signal and the set of resource elements is indicative ofan identifier. Tire one or more processors are further configured to,while being served by a second network node distinct from the firstnetwork node, receive a reference signal in said specific resourceelement from the second network node and transmit feedback informationto the second network node. The reference signal or the combination ofthe reference signal and the set of resource elements is indicative ofan identifier, and the wireless device is configured to receive thereference signal with different beamforming from the first and secondnetwork nodes in spite of equality of the identifiers.

According to certain embodiments, a computer program product comprisinginstructions stored on non-transient computer-readable media which, whenexecuted by a processor, performs the acts of: selecting a subset from apredetermined set of P CSI-RS ports for receiving channel information,wherein each CSI-RS port corresponds to a combination of a set ofresource elements and an antenna port of an antenna array, thepredetermined set comprises a first number P₁ of CSI-RS ports with afirst polarization state and a second, number P₂ of CSI-RS ports with asecond polarization state, the first, and second polarization statesbeing distinct, and populating the subset with Q CSI-RS ports in suchmanner that the ratio of CSI-RS ports respectively having the first andsecond polarization states is equal to the ratio of the first and secondnumbers.

According to certain embodiments, a computer program product, comprisinginstructions stored on non-transient computer-readable media which, whenexecuted by a processor, performs the acts of: while being served by afirst network node, receiving a reference signal in a set of specificresource elements from the first network node and transmitting feedbackinformation to the first network node, wherein the reference signal orthe combination of the reference signal and the set of resource elementsis indicative of an identifier; and while being served by a secondnetwork node distinct from the first network node, receiving a referencesignal in said set of specific resource elements from the second networknode and transmitting feedback information to the second network node,wherein the reference signal or the combination of the reference signaland the set of resource elements is indicative of an identifier. Thereference signal is received with different beamforming from the firstand second network nodes in spite of equality of the identifiers.

According to certain embodiments, a computer program product comprisinginstructions stored on non-transient computer-readable media which, whenexecuted by a processor, performs the acts of: receiving, from a networknode, a CSI-RS setup comprising K CSI reference signal configurationseach with N CSI-RS ports and an antenna configuration of the networknode with P antenna ports, wherein the network node is equipped with P=8or P>8 antenna ports for transmitting signals to the wireless device;determining a subset of Q antenna ports from the P antenna ports;measuring channel information based on the reference signals associatedthe subset of antenna ports; and reporting the measured channelinformation to the network node.

Certain embodiments of the present disclosure may provide one or moretechnical advantages. As one example, certain embodiments mayadvantageously not require additional signaling for configuring CSI-RSports for periodic CSI reporting. As another example, legacy terminalscan be supported with the same eNB antenna array as FD-MIMO supportingterminals without additional CSI-RS overhead, since the ports used forfirst type of feedback is a subset of the ports used for second type offeedback. As yet another example, the codebooks, which are designed forcross polarized antenna arrays where the first half of antenna ports areon one polarization and the second half of antenna ports are on adifferent, polarization, can be used both for the first type and thesecond type of feedback.

Modifications, additions, or omissions may be made to the systems andapparatuses described herein without departing from the scope of thedisclosure. The components of the systems and apparatuses may beintegrated or separated. Moreover, the operations of the systems andapparatuses may be performed by more, fewer, or other components.Additionally, operations of the systems and apparatuses may be performedusing any suitable logic comprising software, hardware, and/or otherlogic. As used in this document, “each” refers to each member of a setor each member of a subset of a set.

Modifications, additions, or omissions may be made to the methodsdescribed herein without departing from the scope of the disclosure. Themethods may include more, fewer, or other steps. Additionally, steps maybe performed in any suitable order.

Although this disclosure has been, described in terms of certainembodiments, alterations and permutations of the embodiments will beapparent to those skilled in the art. Accordingly, the above descriptionof the embodiments does not constrain this disclosure. Other changes,substitutions, and alterations are possible without departing from thespirit and scope of this disclosure, as defined by the following claims.

Abbreviations used in the preceding description include:

ARQ Automatic Retransmission Request

CQI Channel Quality Indicators

CSI Channel State Information

CSI-RS Channel State Information Reference Signals

DFT Discrete Fourier Transform

LTE Long Term Evolution

MIMO Multiple Input Multiple Output

OCC Orthogonal Cover Code

OFDM Orthogonal Frequency Division Multiplexing

PMI Precoding Matrix Indicator

PUCCH Physical Uplink Control Channel

RI Rank Indicator

SINR Signal to interference plus Noise Ratio

TFRE Time Frequency Resource Element

UE User Equipment

The invention claimed is:
 1. A method in a network node of selecting asubset of Channel State Information-Reference Signal (CSI-RS) ports froma predetermined set of P CSI-RS ports for receiving channel information,wherein P is an integer equal to or greater than 2, and wherein: thenetwork node is a network node of a wireless communication network andcomprises an antenna array with controllable polarization; each CSI-RSport corresponds to a combination of a set of resource elements and anantenna port of said antenna array; and the predetermined set of theCSI-RS ports comprises a first number P₁ of CSI-RS ports with a firstpolarization state and a second number P₂ of CSI-RS ports with a secondpolarization state, the first and second polarization states beingdistinct, the method comprising: populating the subset of CSI-RS portswith Q CSI-RS ports in such manner that a ratio of CSI-RS portsrespectively having the first and second polarization states is equal tothe ratio of the first and second numbers, wherein Q≤P; determiningwhether feedback of a first type or a second type is enabled; iffeedback of the first type is to be enabled, transmitting referencesignals on CSI-RS ports from the subset for periodic CSI reporting; andif feedback of the second type is to be enabled, transmitting referencesignals on CSI-RS ports from the predetermined set for aperiodic Class-ACSI reporting, wherein each CSI-RS port in the predetermined set isassociated with an identifier, and wherein one of the following holds:the identifier is explicitly stated in a feedback signal; the identifieris implicitly derivable from an internal structure of a feedback signal;and the identifier is implicitly derivable from a resource used fortransmitting a feedback signal.
 2. The method of claim 1, wherein thesubset is populated with QP₁/(P₁+P₂) CSI-RS ports having the firstpolarization state and QP₂/(P₁+P₂) CSI-RS ports having the secondpolarization state.
 3. The method of claim 1, wherein P₁−P₂ whereby thesubset is populated with equal proportions of CSI-RS ports with thefirst and second polarization states.
 4. The method of claim 1, whereinP₁+P₂=P.
 5. The method of claim 4, whereby half of the CSI-RS ports inthe subset have the first polarization state and half of the CSI-RSports in the subset have the second polarization state.
 6. The method ofclaim 1, wherein: the CSI-RS ports with a first polarization state areassociated with identifiers in a first predetermined range, and theCSI-RS ports with a second polarization state are associated withidentifiers in a second predetermined range, and one of the followingholds: (i) the subset is populated with Q/2 CSI-RS ports from a lowerportion of the first predetermined range and Q/2 CSI-RS ports from alower portion of the second predetermined range; (ii) the subset ispopulated with Q/2 CSI-RS ports from a higher portion of the firstpredetermined range and Q/2 CSI-RS ports from a higher portion of thesecond predetermined range.
 7. The method of claim 6, wherein eachCSI-RS port is associated with an identifier being a port number p givenby $\begin{matrix}{p = \left\{ \begin{matrix}{r + {\frac{N}{2}k}} & {{r = 15},16,\ldots\;,{14 + \frac{N}{2}}} \\{r + {\frac{N}{2}\left( {k + K - 1} \right)}} & {{r = {15 + \frac{N}{2}}},\ldots\;,{14 + N}}\end{matrix} \right.} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$ where K is a number of CSI reference signalconfigurations, k is any integer in [O, K−1]N is the number of antennaports or reference signals in each of the K configurations, and r is anyinteger in [15,14+N].
 8. The method of claim 7, wherein the subsetconsists of CSI-RS ports with port numbers given by Eq.
 1. 9. The methodof claim 7, wherein the subset is populated with Q CSI-RS portsassociated with port numbers given by $p = \left\{ \begin{matrix}{r + {\frac{N}{2}k}} & {{r = 15},16,\ldots\;,{14 + \frac{N}{2}}} \\{r + {\frac{N}{2}\left( {k + K - 1} \right)}} & {{r = {15 + \frac{N}{2}}},\ldots\;,{14 + N}}\end{matrix} \right.$ where k is restricted to$\left\lbrack {0,{\frac{Q}{N} - 1}} \right\rbrack$ and Q≥N.
 10. Themethod of claim 6, further comprising: associating the CSI-RS ports withalternative identifiers, which are selected from the ordered set andsusceptible of enabling the network node to identify a first type offeedback relating to a CSI reference signal transmitted by the networknode on a CSI-RS port.
 11. The method of claim 10, wherein theidentifiers define an ordering of the CSI-RS ports, which is preservedby the alternative identifiers.
 12. The method of claim 11, wherein thealternative identifiers are consecutive.
 13. The method of claim 10,where the alternative identifiers p’ are given by$p^{\prime} = \left\{ \begin{matrix}{{p,}\mspace{121mu}} & {{q = 0};} \\{{p - \frac{{KN} - Q}{2}},} & {q = 1.}\end{matrix} \right.$ where q=0 is for the first polarization state andq=1 is for the second polarization state.
 14. The method of claim 1,wherein: each CSI-RS port in the predetermined set is associated with anidentifier selected from an ordered set; the first number P₁ of CSI-RSports are associated with identifiers in a first predetermined range andthe second number P₂ of CSI-RS ports are associated with identifiers ina second predetermined range; and said populating comprises populatingthe subset with a number of CSI-RS ports from a lower portion of thefirst predetermined range and an equal number of CSI-RS ports from alower portion of the second predetermined range, each CSI-RS port in thesubset being associated with an identifier that is a port number p givenby $\begin{matrix}{p = \left\{ {\begin{matrix}{r + {\frac{N}{2}k}} & {{r = 15},16,\ldots\;,{14 + \frac{N}{2}}} \\{r + {\frac{N}{2}\left( {k + K - 1} \right)}} & {{r = {15 + \frac{N}{2}}},\ldots\;,{14 + N}}\end{matrix},} \right.} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$ where K is a number of CSI reference signalconfigurations, k is any integer in [0,K−1], N is the number of antennaports or reference signals in each of the K configurations, and r is anyinteger in [15,14+N].
 15. The method of claim 1, further comprising:receiving feedback from a wireless device in the wireless communicationnetwork.
 16. The method of claim 1, wherein the CSI-RS ports with thefirst polarization state differ from the CSI-RS ports with the secondpolarization state in that a first co-phasing coefficient is applied tothe CSI-RS ports with the first polarization state and a distinct secondco-phasing coefficient is applied to the CSI-RS ports with the secondpolarization state.
 17. A method in a wireless device served by anetwork node of a wireless communication network, the method comprising:receiving, from the network node, a Channel State information-ReferenceSignal (CSI-RS) setup comprising K CSI-RS configurations, wherein K>1and each CSI-RS configuration is comprising N CSI-RS ports and anantenna configuration of the network node with P antenna ports, whereinN is defined in 1<N<P and multiple of 2; determining a subset of Qantenna ports from the P antenna ports, wherein Q<P; determining whetherfeedback of a first type or a second type is enabled; if feedback of thefirst type is enabled, measuring channel information based on thereference signals associated with the subset of antenna ports forperiodic CSI reporting; if feedback of the second type is enabled,measuring channel information based on signals associated with the Pantenna ports for aperiodic Class-A CSI reporting; and reporting themeasured channel information to the network node, wherein each CSI-RSport in the predetermined set is associated with an identifier, andwherein one of the following holds: the identifier is explicitly statedin a feedback signal; the identifier is implicitly derivable from aninternal structure of a feedback signal; and the identifier isimplicitly derivable from a resource used for transmitting a feedbacksignal.
 18. The method of claim 17, wherein: the antenna configurationof the CSI-RS setup comprises P CSI-RS ports; said determining a subsetof Q ports comprises determining a first subset of P/2 CSI-RS ports anda second subset of P/2 CSI-RS ports from the P CSI-RS ports, wherein:the first subset comprises N/2 CSI-RS ports from each of the K CSI-RSconfigurations; and the second subset comprises the remaining N/2 CSI-RSports from each of the K CSI-RS configurations.
 19. The method of claim18, wherein: the first subset corresponds to a first length-P/2 vectorin a codebook used for state information feedback, the vector beingselected from a set of possible values in the codebook; the secondsubset corresponds to a second length-P/2 vector obtainable by scalingthe first length-P/2 vector by a complex number.
 20. The method of claim18, wherein the determining comprises forming the first subset as CSI-RSports indexed by${p = {{r + {\frac{N}{2}k\mspace{14mu} r}} = 15}},16,\ldots\;,{14 + \frac{N}{2}},$and forming the second subset as CSI-RS ports indexed by${{p = {r + {\frac{N}{2}\left( {k + K - 1} \right)}}};{r = {15 + \frac{N}{2}}}},\ldots\;,{14 + N},$wherein, for both subsets, k runs over the K CSI-RS configurations suchthat k=0, 1, . . . K−1.
 21. The method of claim 17, wherein themeasuring and reporting are performed periodically if feedback of thefirst type is enabled.
 22. The method of claim 17, wherein thedetermining comprises deriving the Q antenna ports, which ports areindexed by $p = \left\{ \begin{matrix}{r + {\frac{N}{2}k}} & {{r = 15},16,\ldots\;,{14 + \frac{N}{2}}} \\{r + {\frac{N}{2}\left( {k + K - 1} \right)}} & {{r = {15 + \frac{N}{2}}},\ldots\;,{14 + N}}\end{matrix} \right.$ where k is restricted to$\left\lbrack {0,{\frac{Q}{N} - 1}} \right\rbrack.$
 23. The method ofclaim 22, wherein the indices of the derived Q antenna ports arere-ordered such that the second set of $\frac{Q}{2}$ ports${p = {r + {\frac{N}{2}\left( {k + K - 1} \right)}}},{{{where}\mspace{14mu} r} = {15 + \frac{N}{2}}},\ldots\;,{14 + N},$are re-indexed as ports$\left\{ {{15 + \frac{Q}{2}},\ldots\;,{15 + Q}} \right\}.$
 24. A networknode comprising: an antenna array with controllable polarization; andone or more processors, the one or more processors configured to: selecta subset of Channel State Information-Reference Signal (CSI-RS) portsfrom a predetermined set of P CSI-RS ports for receiving channelinformation, wherein P is an integer equal to or greater than 2, whereinthe predetermined set of P CSI-RS ports comprises a first number P₁ ofCSI-RS ports with a first polarization state and a second number P₂ ofCSI-RS ports with a second polarization state, wherein the first andsecond polarization states are distinct, and wherein each CSI-RS portcorresponds to a combination of a set of resource elements and anantenna port of said antenna array; populate the subset with Q CSI-RSports in such manner that the ratio of CSI-RS ports respectively havingthe first and second polarization states is equal to the ratio of thefirst and second numbers; determine whether feedback of a first type ora second type is enabled; if feedback of the first type is to beenabled, transmit reference signals on CSI-RS ports from the subset ofCSI-RS ports for periodic CSI reporting; and if feedback of the secondtype is to be enabled, transmit reference signals on CSI-RS ports fromthe predetermined set of CSI-RS ports for aperiodic Class-A CSIreporting, wherein each CSI-RS port in the predetermined set isassociated with an identifier, and wherein one of the following holds:the identifier is explicitly stated in a feedback signal; the identifieris implicitly derivable from an internal structure of a feedback signal;and the identifier is implicitly derivable from a resource used fortransmitting a feedback signal.
 25. A wireless device configured to beserved by a network node in a wireless communication network, thewireless device comprising: one or more processors, the one or moreprocessors configured to: receive, from the network node, a ChannelState information-Reference Signal (CSI-RS) setup comprising K CSI-RSconfigurations, wherein K>1 and each CSI-RS configuration is comprisingN CSI-RS ports and an antenna configuration of the network node with Pantenna ports, wherein N is defined in 1<N<P and multiple of 2;determine a subset of Q antenna ports from the P antenna ports, whereinQ<P; determine whether feedback of a first type or a second type isenabled; if feedback of the first type is to be enabled, measure channelinformation based on the reference signals associated with the subset ofQ antenna ports for periodic CSI reporting; if a feedback of the secondtype is to be enabled, measure channel information based on thereference signals associated with the P antenna ports for aperiodicClass-A CSI reporting; and report the measured channel information tothe network node, wherein each CSI-RS port in the predetermined set isassociated with an identifier, and wherein one of the following holds:the identifier is explicitly stated in a feedback signal; the identifieris implicitly derivable from an internal structure of a feedback signal;and the identifier is implicitly derivable from a resource used fortransmitting a feedback signal.